poj 1113Wall
http://poj.org/problem?id=1113
1 #include<cstdio> 2 #include<cstring> 3 #include<cstdlib> 4 #include<cmath> 5 #include<algorithm> 6 using namespace std; 7 8 const int maxn=5000; 9 const double pi=acos(-1.0); 10 11 struct point 12 { 13 double x,y; 14 bool operator <(const point &a)const 15 { 16 return (x<a.x)||(x==a.x&&y<a.y); 17 } 18 }p[maxn],ch[maxn]; 19 20 double sqr(double x) 21 { 22 return x*x; 23 } 24 25 double det(point a,point b,point c) 26 { 27 return ((b.x-a.x)*(c.y-a.y)-(c.x-a.x)*(b.y-a.y)); 28 } 29 30 double dis(point a,point b) 31 { 32 return sqrt(sqr(a.x-b.x)+sqr(a.y-b.y)); 33 } 34 35 int convex_hull(point *p,int n,point *ch) 36 { 37 sort(p,p+n); 38 int m=0; 39 for(int i=0; i<n; i++) 40 { 41 while(m>1&&det(ch[m-2],ch[m-1],p[i])<=0) m--; 42 ch[m++]=p[i]; 43 } 44 int k=m; 45 for(int i=n-2; i>=0; i--) 46 { 47 while(m>k&&det(ch[m-2],ch[m-1],p[i])<=0) m--; 48 ch[m++]=p[i]; 49 } 50 if(n>1) m--; 51 return m; 52 } 53 54 double diss(point *ch,int n) 55 { 56 double sum=0; 57 for(int i=1; i<n; i++) 58 { 59 sum+=dis(ch[i],ch[i-1]); 60 } 61 return sum; 62 } 63 int main() 64 { 65 int n,l; 66 scanf("%d%d",&n,&l); 67 for(int i=0; i<n; i++) 68 { 69 scanf("%lf%lf",&p[i].x,&p[i].y); 70 } 71 int cn=convex_hull(p,n,ch); 72 printf("%.lf\n",(diss(ch,cn+1)+2*pi*l)); 73 return 0; 74 }
